1. Field of the Invention
The present invention relates to a magnetic head/disk testing apparatus (which is referred to hereinafter as a head tester) for testing a magnetic head and/or a magnetic disk, both being significant functional parts of a magnetic disk drive or magnetic disk storage device. The present invention also relates to a method for testing a magnetic head/disk.
2. Description of the Related Art
A magnetic disk storage device (which is referred to hereinafter as an HDD) is a mass storage random access memory device in which digital data is written on or read from a magnetic disk medium (platter) which rotates at high speed, by a magnetic head which is located above and close to the magnetic disk medium. In recent years, HDDs have been miniaturized so as to achieve dramatically increased storage data capacity in order to meet demands of a technetronic society and as a result of technological competition. An increase in the storage capacity for the same shape and size can be achieved by increasing the magnetic recording density of the magnetic disk medium.
The magnetic recording density (areal density: Gbpsi (gigabits per square inch)) is the product of the linear density (density in the circumferential direction: bpi (bit per inch)) and the track density (density in the radial direction: TPI (track per inch)). The magnetic recording density of a typical HDD at present is approximately 10 Gbpsi (=500K bpi (linear density)xc3x9720K TPI (track density). However, the current target recording density is 100 Gbpsi, and it is expected that the recording density will be increased to approximately 1000 Gbpsi in the near future. In the so-called xe2x80x98horizontal magnetic recording technologyxe2x80x99, the linear density is coming to its limit due to thermally induced self-demagnetization phenomenon and the like. Therefore, attempts have been made to increase the track density. For example, if the track density of 20K TPI is increased to the value of the linear density, i.e., approximately 500K TPI, the areal density would be increased 25 times, i.e., to approximately 250 Gbpsi.
A head tester is composed of a spin stand and an analyzer. In order to simulate the head working environment within HDDs, the spin stand is equipped with an extremely high precision air bearing spindle motor to rotate the disk medium, and a test head holding and positioning mechanism. The analyzer generates and writes the data, and reads the data back for signal analysis.
However, the currently available head testers cannot satisfactorily cope with recent advancements in HDD technology, for example, the increasing bit rate, and the radial positioning accuracy in testing very narrow width heads.
While HDDs employ embedded servo technology (or sector servo technology) in order to accurately position the heads on tracks, the spin stand in the conventional head testers rely on the mechanical accuracy without using sector servo technology. However, such an approach is reaching a limit against the recent increase of HDD track density.
The relationship of the track density, the track pitch, the head track width, and the required positioning accuracy is shown below.
The main causes of positioning error of the magnetic head are:
(1-1) Aperiodic axis fluctuation of the spindle motor (NRRO: non-repeatable run-out).
(1-2) Positioning error of the magnetic head holding mechanism and the magnetic head itself due to vibration, etc.
(1-3) Vibration of the magnetic disk and the magnetic head due to air flow turbulence above the magnetic disk which rotates at a high speed.
In conventional magnetic head testers, attempts have been made to improve the positioning accuracy by combining a vibration-proof table, an air-bearing spindle motor, a piezo actuator, and an air flow straightening vane, etc.
Such a conventional solution, however, requires high cost and space and, furthermore, since the required accuracy level has increased, is reaching its limit in accuracy.
The accuracy limit achievable by the above described conventional solution is said to be 50 kTPI, and the test accuracy deteriorates as track density reaches this limit.
As an alternative solution, it is possible to utilize tracking control technology on a head tester by applying sector servo technology which is used in HDD products, although in practice such a head tester has not been provided on the market. Sector servo technology achieves high precision positioning by using a method wherein high precision track position data is written in advance on the magnetic disk at a designated format, and the written data is read every moment (read constantly) by the magnetic head being tested, in order to correct the positioning error (tracking control).
For that purpose, the following needs to be achieved:
(2-1) An accurate track position data writing function (servo track writing function); and
(2-2) A rigid actuator for high speed tracking.
To meet the requirements stipulated in (2-1) and (2-2) above, the spin stand must be provided with a high precision servo track write function. Though a high precision air bearing spindle motor can be used in the spin stand, the tracking capability is limited in the spin stand due to the increased mass of head holding fixture. Due to these restrictions, the maximum achievable track density by utilizing tracking control technology by applying sector servo technology is approximately 200 kTPI.
The object of the present invention is to achieve a test method for magnetic head or magnetic disk having a dramatically improved test capability for very narrow track width head.
To achieve the above object, a testing apparatus is provided for a magnetic head or a magnetic disk, including a magnetic disk which rotates at a predetermined constant rotational speed; a magnetic head moving mechanism which holds a magnetic head and which moves the magnetic head to a predetermined position in a radial direction of the magnetic disk; a movement mechanism control device for driving the magnetic head moving mechanism, wherein the movement mechanism control device moves the magnetic head moving mechanism to a predetermined radial position corresponding to position data; a read/write control device for writing a predetermined magnetic signal on the magnetic disk using the magnetic head, and for reading a magnetic signal of the magnetic disk using the magnetic head; and a memory for storing therein position data embedded in a data surface of the magnetic disk, extracted from the magnetic signal which is read by the read/write control device.
The test method for magnetic disk or head of the present invention is characterized by a magnetic disk that rotates in a predetermined constant speed, a magnetic head moving mechanism that holds and radially moves the head under test, a writing capability for servo track data on the disk, writing and reading capabilities of predetermined data to and from the disk at data field of the servo format, an extracting capability of position data from the read back signal, storing and reporting capabilities of the above extracted position data, and a method that compensates the test results using the above extracted and stored position data from the disk.
In an embodiment, the method is applied to a track profile test, the method including a pre-erasure step in which the magnetic head is moved to a predetermined test position in the radial direction by the magnetic head moving mechanism, so that each sector data in a predetermined test range of tracks of a predetermined format on the magnetic disk by the magnetic head which has been moved to the predetermined test position is erased, the erasure operations being repeatedly carried out at a plurality of positions while moving the magnetic head at a predetermined pitch in the radial direction; a signal writing step in which the magnetic head is moved to a substantially central position in the radial direction, of the test range which has been subjected to the erasure operation, so that a predetermined signal is written in the sector of the test range at the substantially central position; and a signal reading step in which the signal written in the sector in the predetermined test range is read while moving the magnetic head at a predetermined pitch, within a predetermined radial range on opposite sides of the substantially central position in the radial direction, through the magnetic head moving mechanism.
In an embodiment, the testing method including a pre-erasure step in which the magnetic head is moved to a predetermined test position in the radial direction by the magnetic head moving mechanism, so that each sector data in a predetermined test range of tracks of a predetermined format on the magnetic disk by the magnetic head which has been moved to the predetermined test position is erased, the erasure operations being repeatedly carried out at a plurality of positions while moving the magnetic head at a predetermined pitch in the radial direction; a signal writing step in which the magnetic head is moved to a target position in the radial direction, of the test range which has been subjected to the erasure operation, so that a low frequency signal is written in the sectors of the test range; a low frequency signal reading step in which the low frequency signal written in the sectors in the predetermined test range is read by the magnetic head which is moved through the magnetic head moving mechanism to a position which is determined taking into account the target position and a read/write offset of the magnetic head, wherein the amplitude of the read low frequency signal is stored in the memory; a high frequency signal writing step in which the magnetic head is moved by the magnetic head moving mechanism to a position which is determined taking into account the target position and the read/write offset of the magnetic head to write the high frequency signal in the sectors within the predetermined test range; a high frequency signal reading step in which the high frequency signal written in the predetermined test range is read by the magnetic head which is moved through the magnetic head moving mechanism to a position which is determined taking into account the target position and a read/write offset of the magnetic head; and a data selection step in which effective sectors are selected based on the position data of the signal read at each of the signal reading steps.
In an embodiment, the pre-erasure step includes checking whether the pre-erasure is valid, by successively marking the radial areas which have been subjected to erasure, for the circumferential area of each sector of the measurement range included in the test area which has been subjected to the pre-erasure included in the test range, based on the position data stored at each erasure step; and erasing the radial area by moving the magnetic head to the radial area which is not valid in the case where the pre-erasure of the radial area is not invalid.
In an embodiment, the pre-erasure step includes checking whether the radial areas that have been subjected to erasure overlap, for the circumferential area of each sector of the measurement range included in the test area which has been subjected to the pre-erasure included in the test range, based on the position data stored at each erasure step; and wherein in the case where the radial areas overlap, the radial areas are deemed to be one radial area; and in the case where the circumferential data areas of the sectors within the measurement area are not integrated into one radial erasure area, the magnetic head is moved to an area between the radial areas which do not overlap, so that a predetermined signal is written in the radial area to thereby integrate the circumferential data areas of the sectors within the measurement area into one radial erasure area.
In an embodiment, when the read/write operation of the data from/on the magnetic disk by the magnetic head is carried out by the magnetic head, the magnetic head moving mechanism is driven to move and follow the magnetic head so that the position information embedded in the data surface, read and extracted from the magnetic disk by the magnetic head is identical to a predetermined target position.
In an embodiment, wherein the signal reading step includes moving the magnetic head in one of cyclically and irregularly in the radial direction by providing a predetermined swing to the magnetic head moving mechanism.
In an embodiment, the testing method further includes a calculation step to obtain a radial deviation between the writing operation and the reading operation, based on the position information of the magnetic head which has been judged to be valid in the pre-erasure validity checking operation and the read signal information corresponding to the magnetic head position information.
In an embodiment, the testing method includes servo-writing the data on the magnetic disk which rotates at a speed at which aperiodic position error is minimized, via one of a reference clock magnetic head and the writing magnetic head, in a predetermined range larger than the radial test area the magnetic disk, prior to the pre-erasure step.
In an embodiment, the magnetic head includes a plurality of magnetic heads in the form of a head stack assembly.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-277893 (filed on Sep. 13, 2000) which is expressly incorporated herein by reference in its entirety.